Device for vacuum packaging, particularly of food products

ABSTRACT

A packaging device, particularly for manually or automatically packaging trays containing food products or technical materials which can be inserted, by means of a loading platform, between longitudinally folded parts of a single-folded film and comprising elements for thermal bonding or heat-sealing for sealing, and at least one nozzle for producing a vacuum and/or for introducing the gas or mixture, and a vacuum chamber. The single-folded film is fixed and the vacuum chamber is movable and comprises at least one movable presser arranged above the single-folded film. The presser is forced on top of the tray and is provided with elements adapted to convey the streams of air and/or gas. The return of air into the vacuum chamber occurs by means of a series of holes provided between a transverse heat-sealing bar and the wall of the vacuum chamber that is parallel thereto.

TECHNICAL FIELD

The present application relates to a packaging device, particularly for packaging food products and technical materials.

BACKGROUND ART

Currently, vacuum machines are known which have a bell-shaped chamber and comprise a vacuum pump connected to a chamber, also known as a vacuum chamber, and inside which a preformed pouch, which is open on three sides, is usually arranged, a food product being placed inside it.

In these machines of the known type, the preformed pouch, with the product already inside it, is then placed inside the vacuum chamber and vacuum is then produced inside the chamber; then heat-sealing is performed at the free side of the preformed pouch.

This known technology entails the need to use preformed pouches, which thus have one size that is comparable to the dimensions of the product; moreover, considerable labor is required.

Thus, there are operating steps that extend the time required to achieve vacuum packaging of the product; moreover, if packaging occurs in a controlled atmosphere, there is a waste of most of the gas because the gas is dispersed not only in the pouch but also and mostly inside the vacuum chamber.

EP603704 is also known in which the packaging of food products occurs by using a film made of plastic material, which is conveyed through a folding station in order to obtain a double layer and is then heat-sealed so as to define pockets.

These pockets are obtained in the desired size or capacity before being filled and sealed.

Heat-sealing and forming are followed by filling and by the closing and cutting of the pockets or pouches thus obtained: this solution, however, is complicated, in that it involves multiple and separate stations for performing the individual operations to which the film made of plastic material must be subjected in sequence.

Moreover, the above solution involves a hot or a cold forming of the plastic film and the filling, by means of a nozzle, of liquid products, flours or finely granulated materials, and therefore it is not possible to consider the use of the illustrated solution for solid products having predetermined volumes such as sliced meats, meat, portioned cheeses, and trays containing food and non-food products.

In the described known solution, moreover, in order to achieve the closure of the pocket or pouch it is necessary to make the pocket or pouch pass through various operating steps, with the consequent need for optimum centering of the pouch at each station so as to allow the optimum and desired processing.

EP0405718 is also known which describes a solution that illustrates a packaging device, particularly for packaging food products or technical materials that can be inserted between longitudinally folded parts of a single-folded film from an open side thereof, the device comprising means for thermal bonding or heat-sealing which are substantially L-shaped in order to seal the film both at the open longitudinal side and at its transverse sides, and at least one nozzle for producing vacuum and/or for introducing the gas or mixture.

EP0832819B1 is also known whose priority is Italian Patent Application AL960002 dated Sep. 26, 1996 and which illustrates a packaging device which comprises a vacuum chamber that can be opened to receive a length of at least one single-folded film with the material to be packaged inserted therein and can be respectively closed hermetically, after which it is possible to produce the vacuum and/or introduce the gas or mixture with the portion or length of film which assumes a pocket-like shape, heat-sealing means being furthermore provided which are arranged for operation inside the vacuum chamber, the at least one nozzle being arranged at the vacuum chamber so as to face, after being closed, toward the open longitudinal and/or transverse sides of the film length.

This solution, too, is not free from drawbacks, since it has been found that micro-creases form during the step of heat-sealing the film and this may cause problems in the seal and it worsens the aesthetic appearance of the packaging.

Moreover, the flow of gas inside the film is not optimum, thus lowering the efficiency of the device.

Finally, when the operator pulls away the sheet, the sheet may assume an incorrect arrangement.

Another problem is also noted: when a vacuum is provided in a bell, and therefore inside the pouch being formed, it is then necessary to compensate the vacuum partially with gas; however, if the compensation is excessive, the bell opens during the heat-sealing step.

Since one is working with a system with a particularly variable equilibrium, there is no precise control of the volume of gas introduced in the pouch or bag being formed.

The quantity, in absolute values and in relative values (%), of gas that remains inside the pouch being formed is thus extremely variable and difficult to control, and this produces a series of pouches or packages that are more or less inflated or deflated, depending on the individual case.

The problem then worsens if it is necessary to often change the format of the packaging.

Another problem is observed during the heat-sealing step of the film that is heat-sealed and cut on the transverse side, with respect to the direction of advancement of the film itself: since it is often made of heat-shrinking material, the film can shrink, reducing its width, and this might prevent the accommodation of the incoming tray.

The tray can thus arrive and find an insufficient space to accommodate it, and this causes its redirection toward the open side of the pouch, ending up on the longitudinal heat-sealing bar, causing machine downtimes and lost time for cleaning it.

Finally, it is noted that the return of air into the bell or vacuum chamber occurs, for constructive reasons, usually in a region far from the heat-sealing bar or it coincides with the vacuum port by means of the use of a three-way valve, but this does not optimize the conveyance of the flow inside the bell.

DISCLOSURE OF THE INVENTION

The aim of the present invention is to solve the above-mentioned technical problems, eliminating the drawbacks of the cited background art, by providing a device that makes it possible to obtain a vacuum packaging or a compensated vacuum packaging of technical products or food products such as sliced meats, meat, portioned cheeses, trays that contain food and non-food products, thus making it possible to optimize the gas inside the pouch so that uniformly inflated pouches or packages are obtained.

Within this aim, an object of the present solution is to provide a device that can be used even by an operator who is not specially trained in the adjustments of format changes.

Another object is to provide a device that allows the optimum insertion of the tray in the single-folded film, previously heat-sealed and cut on the transverse side,

Another object is to provide a device that allows the optimum insertion of the tray in the pouch, thus avoiding machine downtimes and lost time for cleaning it.

Another object is to provide a device that adds to the preceding characteristics that of being structurally simple, reliable and safe in use.

This aim and these objects, as well as others that will become better apparent hereinafter, are achieved by a packaging device, particularly for manually or automatically packaging trays containing food products or technical materials which can be inserted, by means of a loading platform, between longitudinally folded parts of a single-folded film and comprising means for thermal bonding or heat-sealing for sealing, and at least one nozzle for producing a vacuum and/or for introducing the gas or mixture, and a vacuum chamber, characterized in that said single-folded film is fixed and said vacuum chamber is movable transversely to the direction of insertion of said trays and comprises at least one presser, movable over said single-folded film, which is forced on top of said trays and is provided with means adapted to convey the streams of air and/or gas, the return of air into said vacuum chamber occurring by means of a series of holes provided between a transverse heat-sealing bar, which constitutes said thermal bonding means, and the wall of said vacuum chamber that is parallel thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become better apparent from the following detailed description of four particular embodiments, illustrated by way of non-limiting example in the accompanying drawings, wherein:

FIG. 1 is a side perspective view of a device in its embodiments;

FIG. 2 is a sectional view of the device, taken along the line II-II of FIG. 1, in the condition in which the vacuum chamber is open;

FIG. 3 is a view, similar to the preceding one, of the condition in which, with the vacuum chamber open, the tray placed inside the single-folded film is inserted;

FIG. 4 is a view, similar to the preceding one, of the condition in which the vacuum chamber is closed and the presser is placed above the single-folded film;

FIG. 5 is a sectional view, taken along the line V-V of FIG. 4;

FIG. 6 is a top view of the device in which, in order to make the drawing more intelligible, the pair of supports for the single-folded film has been omitted;

FIG. 7 is a partially sectional top view of the tray arranged inside the vacuum chamber and of the means adapted to convey the streams of air and/or gas inside it;

FIG. 8 is a sectional view of the device, taken along the line II-II of FIG. 1, in the condition in which the vacuum chamber is open;

FIG. 9 is a view, similar to the preceding one, of the condition in which, with the vacuum chamber open, the tray placed inside the single-folded film is inserted;

FIG. 10 is a view, similar to the preceding one, of the condition in which the vacuum chamber is closed and the presser is placed above the single-folded film;

FIG. 11 is a sectional view, taken along the line XI-XI of FIG. 10;

FIG. 12 is a top view of the device in which, in order to make the drawing more intelligible, the pair of supports for the single-folded film has been omitted;

FIGS. 13 to 15 are partially sectional top views of the vacuum chamber with the tray arranged inside it during the various packaging steps and of the means adapted to convey the streams of air and/or gas inside it.

WAYS OF CARRYING OUT THE INVENTION

With reference to FIGS. 1 to 7, the reference numeral 1 a designates the packaging device particularly for technical materials or food products, which are designated by the reference numeral 2.

The device la comprises a bell-shaped vacuum chamber, designated by the reference numeral 3, which is essentially constituted by a lower container 4 and by an upper lid 5, which can be closed; bands or gaskets 6 for airtightness are arranged perimetrically to the container 4 and the lid 5.

The device uses a single-folded film 7, which thus has a first longitudinal side 8 which is closed and a second longitudinal side 9 which is open.

An L-shaped first heat-sealing bar 10 is arranged within the bell-shaped vacuum chamber 3, with one side adjacent to the inlet 11 of the food product; an essentially L-shaped cutting blade (not shown) is arranged laterally adjacent to the first heat-sealing bar 10 and the lines of the L are arranged respectively parallel to and at right angles to the first heat-sealing bar 10.

The technical materials or food products 2 are stored inside an adapted tray 12, which is placed at a loading platform 13, which is conveniently motorized or movable on suitable means such as, for example, a roller bed.

The single-folded film 7 is kept open by virtue of the presence of a pair of supports 14 a, 14 b, between which the loading platform 13 is interposed; this pair of supports 14 a, 14 b can be moved mutually closer by means of a suitable handwheel 15 which is adapted to adjust their mutual position.

The device 1 a comprises at least one means that is adapted to draw the single-folded film 7, this means being constituted by a suitable motor 16 which actuates a roller 17 which cooperates with a complementary roller 18, the single-folded film 7 being made to pass between these rollers.

The motor 16, the roller 17 and the complementary roller 18 are supported by a suitable arm, which protrudes from a suitable fixed footing 19.

The pair of supports 14 a, 14 b and the handwheel 15, as well as the loading platform 13, are also fixed with respect to the footing 19, so that the single-folded film 7, during its use, can only slide along an axis that is the axis of the loading platform 13, but it is fixed with respect to other possible movements.

The vacuum chamber 3 however can be moved along an axis that is transverse to the direction of advancement of the single-folded film 7, which coincides with the direction of insertion of the tray 12.

The vacuum bell 3 is arranged inside a suitable frame 20 constituted by a pair of uprights 21 a, 21 b and a pair of crossmembers 22 a, 22 b, the latter supporting a pair of first cylinders 23 a, 23 b adapted to move the upper lid 5 and a guide 24 adapted to allow the sliding of the frame 20 at a suitable complementary guide 25 which is integral with the footing 19.

A raised shelf 26 is provided inside the lower container 4, adjacent to the end of the loading platform 13, and is adapted to support the tray 12 inside the vacuum bell 3.

At the upper lid 5 there is internally at least one presser 27, which is movable by means of a pair of suitable second cylinders 28 a, 28 b, which are externally jointly connected to the upper lid 5 in a region adjacent to the upper crossmember 22 a.

A pair of third cylinders 29 a, 29 b and a pair of fourth cylinders 30 a, 30 b are also arranged at the outer surface of the upper lid 5, are arranged along mutually perpendicular directions and are adapted to actuate a second heat-sealing bar 31, which is arranged mirror-symmetrically with respect to the first heat-sealing bar 10.

The presser 27 is provided with means adapted to convey the streams of air and/or gas, these means being constituted by a plurality of ribs 32 which protrude from it in the direction of the tray 12 and are arranged transversely to the direction of advancement of the single-folded film 7.

These ribs 32 are preferably made of rubber, so as to be able to adhere at the edges 33 of the tray 12, thus defining channels 34 adapted to allow the passage of the air and/or gas.

Advantageously, the presser 27 moves jointly with the opening and closing of the bell-shaped vacuum chamber 3. The shape and function of the presser 27 make it possible to better create the vacuum inside the package 35 and allow a better and more constant introduction of the gas inside it.

Moreover, the movement of the presser makes it possible to adapt to the height of the tray 12 and prevents, during the introduction of the gas, the corner 36 of the package 35, which inflates like a balloon, from reaching the upper level of the tray 12: thus having a visible heat seal 37 on the upper window of the package 35 is avoided, thus avoiding a very poor aesthetic appearance that can however be observed in the background art.

The packaging device is further constituted by means adapted to convey the streams of air and/or gas, these means being constituted by a nozzle 38, which is integral with the bell-shaped vacuum chamber 3 and is accommodated hermetically within a box-like appendage 39 provided in two half-shells which protrude laterally to the bell-shaped vacuum chamber 3 along an axis which is perpendicular to the axis of advancement of the single-folded film.

In this manner, the single-folded film 7 is trapped, with the free end 40 of the second longitudinal side 9, which is open, trapped above and below the nozzle, forcing the gas, when it is introduced, to enter the bag that constitutes the package 35, flushing the inside to then flow out into the bell-shaped vacuum chamber 3.

We thus obtain an assurance of vacuum and of the subsequent filling and of the replacement of the air in the bag that contains the product, the use of a long nozzle making it possible to modify easily the size of the bag that constitutes the package 35 by fitting the single-folded film 7 more or less on the nozzle 38 while keeping the drawing system of the single-folded film 7 stationary.

Obviously, the force of the cylinders that keep the bell-shaped vacuum chamber 3 closed is greater than the force of the heat-sealing cylinders, and the frame 20 that supports them is shaped like a closed cage.

It is thus possible to produce a total or partial vacuum, and compensate with gas up to atmospheric pressure, while avoiding, as occurs in the background art, working in highly unstable pressure regions for filling the bag with the gas, the use of the presser making it possible to obtain packages that are identical in the entire batch.

The device comprises, moreover, a plurality of holes 41 for the return of air into the bell-shaped vacuum chamber 3, in order to return it to atmospheric pressure following the heat-sealing of the package 35. These holes 41 are provided between the first heat-sealing bar 10 and the adjacent wall 42 of the bell-shaped vacuum chamber 3.

We thus obtain at the same time the cooling of the heat-seal 37 immediately after heat-sealing, thus preventing the retraction of the package 35.

With reference to the previously cited FIGS. 8 to 15, the reference numeral 1 b designates the device for packaging particularly technical materials or food products, which are designated by the reference numeral 2.

The device 1 b comprises a bell-shaped vacuum chamber, designated by the reference numeral 3, which is essentially constituted by a lower container 4 and by an upper lid 5, which can be closed; bands or gaskets 6 for airtightness are arranged perimetrically to the container 4 and to the lid 5.

The device uses a single-folded film 7, which thus has a first longitudinal side 8 which is closed and a second longitudinal side 9 which is open.

A first transverse heat-sealing bar 10 a is located in proximity to the inlet of the bell-shaped vacuum chamber 3 and, more precisely, inside it, with one side adjacent to the inlet 11 of the food product; a cutting blade (not shown) is arranged laterally adjacent to the first transverse heat-sealing bar 10 a.

The technical materials or food products 2 can be stored inside a suitable tray 12, which is arranged at a loading platform 13, which is conveniently motorized or movable on suitable means such as, for example, a roller bed.

As an alternative, the technical materials or food products 2 may be arranged directly on the loading platform 13 so as to provide packaging directly without the tray 12.

The single-folded film 7 is kept open by virtue of the presence of a pair of supports 14 a, 14 b, between which the loading platform 13 is interposed, the pair of supports 14 a, 14 b being movable mutually closer by means of a suitable handwheel 15 adapted to adjust their mutual position.

The device 1 b further comprises at least one means that is adapted to draw the single-folded film 7, this means being constituted by a suitable motor 16, which actuates a roller 17 which cooperates with a complementary roller 18, the single-folded film 7 being made to pass between these rollers.

The motor 16, the roller 17 and the complementary roller 18 are supported by a suitable arm, which protrudes from a suitable fixed footing 19.

The pair of supports 14 a, 14 b and the handwheel 15, as well as the loading platform 13, are fixed with respect to the footing 19, so that the single-folded film 7, during its use, can only slide along an axis which is the axis of the loading platform 13, but it is fixed with respect to other possible movements.

The vacuum chamber 3 however can be moved along an axis which is transverse to the direction of advancement of the single-folded film 7, which coincides with the direction of insertion of the tray 12.

The vacuum bell 3 is arranged inside a suitable frame 20 constituted by a pair of uprights 21 a, 21 b and by a pair of crossmembers 22 a, 22 b, the latter supporting a pair of first cylinders 23 a, 23 b, which are adapted to move the upper lid 5, and a guide 24, which is adapted to allow the sliding of the frame 20 at a suitable complementary guide 25 which is integral with the footing 19.

A raised shelf 26 is provided inside the lower container 4, adjacent to the end of the loading platform 13, and is adapted to support the tray 12 inside the vacuum bell 3.

At the upper lid 5 there is internally at least one presser 27, which is movable by means of a pair of suitable second cylinders 28 a, 28 b, which are externally jointly connected to the upper lid 5 in a region which is adjacent to the upper crossmember 22 a.

As an alternative, the single-folded film 7 can remain stationary and the bell-shaped vacuum chamber 3 moves with respect to the single-folded film 7.

Again at the outer surface of the upper lid 5 there is a pair of third cylinders 29 a, 29 b, which are adapted to actuate a second transverse heat-sealing bar 31 a, which is arranged mirror-symmetrically with respect to the first transverse heat-sealing bar 10 a.

As an alternative, the first transverse heat-sealing bar 10 a and the second transverse heat-sealing bar 31 a can be arranged outside the bell-shaped vacuum chamber 3.

In this manner, we would obtain advantageously a more slender structure, with the third cylinders 29 a, 29 b arranged outside the bell-shaped vacuum chamber 3, so as to be able to have an increase in the useful volume that can be utilized inside the bell-shaped vacuum chamber 3.

Inside the bell-shaped vacuum chamber 3 there is a first longitudinal heat-sealing bar 10 b, so as to correspond to the open longitudinal side 9 of the single-folded film 7 of the food product, so as to be able to intersect the heat seals performed by the transverse heat-sealing bars 10 a.

Laterally adjacent to the first longitudinal heat-sealing bar 101) there is a cutting blade, and at the outer surface of the lid 5 there is a pair of fourth cylinders 30 a, 30 b adapted to actuate a second longitudinal heat-sealing bar 31 b, which is arranged mirror-symmetrically with respect to the first longitudinal heat-sealing bar lob.

In this manner, it is possible to perform multiple heat seals, one after the other, of the single-folded film 7 along a transverse direction with respect to the sliding direction thereof, so as to prepare multiple trays 12 before performing the vacuum operation, and then the vacuum operation is performed with a single longitudinal heat seal which intersects all the transverse heat seals.

The presser 27 is provided with means adapted to convey the streams of air and/or gas, these means being constituted by a plurality of ribs 32 which protrude therefrom in the direction of the tray 12 and are arranged transversely to the direction of advancement of the single-folded film 7.

These ribs 32 are preferably made of rubber so as to be able to adhere at the edges 33 of the tray 12, defining channels 34 adapted to allow the passage of the air and/or gas.

The presser 27 moves advantageously jointly with the opening and closing of the bell-shaped vacuum chamber 3. The shape and function of the presser 27 makes it possible to better obtain the vacuum inside the package 35 and allows a better and more constant introduction of the gas inside it.

Moreover, the movement of the presser makes it possible to adapt to the height of the tray 12 and prevents, during the introduction of the gas, the corner 36 of the package 35, which inflates like a balloon, from reaching the upper level of the tray 12: thus having a visible heat seal 37 on the upper window of the package 35 is avoided, thus avoiding a poor aesthetic appearance, which can be observed in the background art.

The packaging device is further constituted by means adapted to convey the streams of air and/or gas, these means being constituted by a nozzle 38, which is integral with the bell-shaped vacuum chamber 3 and is accommodated hermetically within a box-like appendage 39 provided in two half-shells which protrude laterally to the bell-shaped vacuum chamber 3 along an axis which is perpendicular to the axis of advancement of the single-folded film.

In this manner, the single-folded film 7 is trapped, with the free end 40 of the second longitudinal side 9 which is open, trapped above and below the nozzle, thus forcing the gas, when it is introduced, to enter the bag that constitutes the package 35, flushing the inside to then flow out into the bell-shaped vacuum chamber 3.

We thus obtain an assurance of vacuum and of the subsequent filling and of the replacement of the air in the bag that contains the product, the use of a long nozzle making it possible to modify easily the size of the bag that constitutes the package 35 by fitting the single-folded film 7 more or less over the nozzle 38, while keeping the drawing system of the single-folded film 7 stationary.

Obviously, the force of the cylinders that keep closed the bell-shaped vacuum chamber 3 is greater than the force of the heat-sealing cylinders, and the frame 20 that supports them is shaped like a closed cage.

It is thus possible to produce a total or partial vacuum and compensate with gas up to atmospheric pressure, while avoiding, as occurs in the background art, working in highly unstable pressure regions for filling the bag with the gas, the use of the presser making it possible to obtain identical packages in the entire batch.

The device comprises, moreover, a plurality of holes 41 for the return of air into the bell-shaped vacuum chamber 3, in order to return it to atmospheric pressure after the heat-sealing of the package 35. These holes 41 are provided between the first heat-sealing transversal bar 10 a and the adjacent wall 42 of the bell-shaped vacuum chamber 3.

We thus obtain, at the same time, the cooling of the heat seal 37 immediately after heat-sealing, thus preventing the retraction of the package 35.

In practice it has been found that the invention has achieved the set aim and objects, a device having being devised which, using a single-folded film, makes it possible to obtain a vacuum or modified-atmosphere package in which the gas inside the bag or pouch that constitutes the package is optimized, so that the packages are uniformly inflated, also making it possible to perform the vacuum operation on multiple trays at the same time.

The possibility to move the bell-shaped vacuum chamber 3 makes it possible to modify the size of the bag or pouch that constitutes the package 35 quickly and easily, since the operator in this case only has to move the position of the frame 20 and thus also the complex of elements associated with the bell-shaped vacuum chamber 3 as a function of the width of the tray 12 to be packaged, and this without touching anything else, with the consequence of having almost nil downtimes.

Obviously, the device can be controlled by suitable mechanical and/or electronic means for predetermining the desired position of the frame 20 in one or more preset points, so that for each type of package 35 it is possible to set, for example by means of a computer, the position of the frame 20 automatically as the package that arrives on the loading platform 13 varies.

The device can thus be used also by an operator who is not particularly trained in the adjustments of format changes and it allows the optimum insertion of the tray in the single-folded film, previously sealed and cut on the transverse side, thus allowing the optimum insertion of the tray in the bag and avoiding machine downtimes and lost time for its cleaning.

Finally, the device is structurally simple, reliable and safe in use.

Obviously, the invention is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

Thus, for example, it is possible to consider keeping the frame 20 fixed and making the single-folded film 7 movable transversely as well with respect to the direction of advancement.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

In the exemplary embodiments that follow, individual characteristics, given in relation to specific examples, may actually be interchanged with other, different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer.

The materials used, as well as the dimensions that constitute the individual components of the invention, may of course be more pertinent according to the specific requirements.

The various means for performing certain different functions certainly need not coexist only in the illustrated embodiment but can be present per se in many embodiments, including ones that are not illustrated.

The characteristics indicated as advantageous, convenient or the like can also be omitted or be replaced with equivalent characteristics.

The disclosures in Italian Patent Applications No. TV2010A000019 and No. TV2010A000117 from which this application claims priority are incorporated herein by reference. 

1-29. (canceled)
 30. A packaging device, particularly for manually or automatically packaging trays containing food products or technical materials which can be inserted, by means of a loading platform, between longitudinally folded parts of a single-folded film and comprising means for thermal bonding or heat-sealing for sealing, and at least one nozzle for producing a vacuum and/or introducing the gas or mixture, and a vacuum chamber, wherein said single-folded film is fixed and said vacuum chamber is movable transversely to the direction of insertion of said trays and comprises at least one presser, movable over said single-folded film, which is forced on top of said trays and is provided with means adapted to convey the streams of air and/or gas, the return of air into said vacuum chamber occurring by means of a series of holes provided between a transverse heat-sealing bar, which constitutes said thermal bonding means, and the wall of said vacuum chamber that is parallel thereto.
 31. The device according to claim 30, wherein said vacuum chamber is a bell-shaped vacuum chamber constituted by a lower container and by a closeable upper lid, bands or gaskets adapted for airtightness being provided perimetrically to said container and to said lid, said single-folded film having a first longitudinal side which is closed and a second longitudinal side which is open, said single-folded film being kept open by the presence of a pair of supports between which said loading platform, motorized or movable on means, is interposed, said pair of supports being movable mutually closer by means of a handwheel adapted to adjust their mutual position.
 32. The device according to claim 30, further comprising at least one means adapted to draw said single-folded film, said means being constituted by a motor which actuates a roller which cooperates with a complementary roller, said single-folded film being made to pass between said rollers, said motor, said roller and said complementary roller being supported by an arm, which protrudes from a fixed footing, with which said pair of supports, said handwheel and said loading platform are also associated.
 33. The device according to claim 30, wherein said bell-shaped vacuum chamber is moved along an axis that is transverse to the direction of advancement of said single-folded film, which coincides with the direction of insertion of a tray that is adapted to contain said technical materials or food products.
 34. The device according to claim 31, wherein said bell-shaped vacuum chamber is arranged inside a frame constituted by a pair of uprights and by a pair of crossmembers, said crossmembers supporting respectively a pair of first cylinders adapted to move said upper lid and a guide adapted to allow the sliding of said frame at a complementary guide which is integral with said footing.
 35. The device according to claim 31, wherein a raised shelf is provided inside said lower container, which is adjacent to the end of said loading platform, and is adapted to support said tray inside said bell-shaped vacuum chamber, at said upper lid there being arranged internally at least one presser, which is movable by means of a pair of second cylinders, which are externally jointly connected to said upper lid in a region that is adjacent to said upper crossmember.
 36. The device according to claim 31, further comprising a first heat-sealing bar, which is L-shaped and arranged within said bell-shaped vacuum chamber, with one side adjacent to an inlet of the food product; a cutting blade being arranged laterally adjacent to said first heat-sealing bar, a pair of third cylinders and a pair of fourth cylinders being arranged at an outer surface of said upper lid and being arranged along mutually perpendicular directions and being adapted to actuate a second heat-sealing bar, which is arranged mirror-symmetrically with respect to said first heat-sealing bar.
 37. The device according to claim 35, wherein said presser is provided with means adapted to convey the streams of air and/or gas, said means being constituted by a plurality of ribs which protrude from it in the direction of said tray and are arranged transversely to the direction of advancement of said single-folded film, said ribs being made of rubber, so as to be able to adhere at the edges of said tray, defining channels adapted to allow the passage of the air and/or gas.
 38. The device according to claim 35, wherein said presser moves jointly with the opening and closing of said bell-shaped vacuum chamber.
 39. The device according to claim 31, further comprising means adapted to convey the streams of air and/or gas, said means being constituted by a nozzle, which is integral with the bell-shaped vacuum chamber and is accommodated hermetically within a box-like appendage provided in two half-shells which protrude laterally to said bell-shaped vacuum chamber along an axis which is perpendicular to the axis of advancement of said single-folded film.
 40. The device according to claim 31, further comprising a plurality of holes for the return of air into said bell-shaped vacuum chamber, to return it to atmospheric pressure following the heat-sealing of a package, said plurality of holes being provided between said first heat-sealing bar and the adjacent wall of said bell-shaped vacuum chamber.
 41. The device according to claim 34, wherein it is controlled by mechanical and/or electronic means for predetermining a desired position of said frame in one or more preset points, so that for each type of package it is possible to set, by means of a computer, the position of said frame automatically as the package that arrives on said loading platform varies.
 42. The device according to claim 34, wherein said frame is also movable transversely with respect to the direction of advancement of said single-folded film.
 43. The device according to claim 30, comprising a loading platform that supports a single-folded film that defines at least two parts which are folded longitudinally to accommodate trays that contain food products and technical materials, thermal bonding or heat-sealing means being comprised which are adapted to seal said folded parts of said single-folded film peripherally with respect to said trays, and at least one nozzle being comprised which is adapted to provide a vacuum and/or adapted to introduce a gas or a mixture in a vacuum chamber that accommodates said trays inserted between said folded parts of said single-folded film, so that said single-folded film and said vacuum chamber are movable with respect to each other transversely to the direction of insertion of said trays in said vacuum chamber, wherein said thermal bonding or heat-sealing means comprise a plurality of independent heat-sealing bars, at least one of them being transverse and at least one of them being longitudinal with respect to the direction of advancement of said single-folded film.
 44. The device according to claim 43, wherein said vacuum chamber is bell-shaped and is provided by a lower container and by an upper lid, which can be closed onto said container, bands or gaskets for airtightness being interposed perimetrically between said container and said lid.
 45. The device according to claim 43, further comprising a pair of supports, which can be moved mutually closer by means of a handwheel adapted to adjust their mutual position in order to open said single-folded film, said loading platform being interposed between said pair of supports, and said single-folded film having a first longitudinal side which is closed and a second longitudinal side which is open.
 46. The device according to claim 45, further comprising at least motor means which are adapted to draw said single-folded film and actuate a roller that cooperates with a complementary roller, said single-folded film being passed between said rollers, said motor means, said roller and said complementary roller being supported by an arm that protrudes from a fixed footing with which said pair of supports, said handwheel and said loading platform are associated.
 47. The device according to claim 43, wherein said vacuum chamber is arranged within a frame constituted by a pair of uprights and by a pair of crossmembers, said crossmembers supporting respectively a pair of first cylinders adapted to move said lid and a guide adapted to allow the sliding of said frame at a guide that is integral with said footing.
 48. The device according to claim 43, wherein said vacuum chamber can move along an axis which is substantially transverse to the direction of advancement of said single-folded film, said substantially transverse axis coinciding with the direction of insertion of said trays.
 49. The device according to claim 43, further comprising at least one presser, which can move above said single-folded film, can engage said trays in an upper region, and is provided with means adapted to convey the streams of air and/or gas.
 50. The device according to claim 49, wherein said means adapted to convey the streams of air and/or gas comprise a plurality of ribs which protrude in the direction of said tray and are arranged transversely to the direction of advancement of said single-folded film, said ribs being made of rubber in order to adhere at the edges of said tray so as to define a plurality of channels adapted to allow the passage of air and/or gas.
 51. The device according to claim 49, wherein inside said container, adjacent to the end of said loading platform, there is a raised shelf, which is adapted to support said tray inside said vacuum chamber, said presser being arranged internally at said lid and being movable by means of a pair of second cylinders, which are externally jointly connected to said lid in a region that is adjacent to said crossmember.
 52. The device according to claim 49, wherein said presser can move jointly with the opening and closing of said vacuum chamber.
 53. The device according to claim 43, further comprising at least one nozzle which is integrally connected to said vacuum chamber, said at least one nozzle being accommodated hermetically within a box-like appendage that is provided in two half-shells that protrude laterally from said vacuum chamber along an axis which is perpendicular to the axis of advancement of said single-folded film.
 54. The device according to claim 51, further comprising a first transverse heat-sealing bar, which is arranged in proximity to an inlet of said vacuum chamber, a cutting blade being laterally adjacent to said first transverse heat-sealing bar, at the outer surface of said lid there being a pair of third cylinders adapted to actuate a second transverse heat-sealing bar, which is arranged mirror-symmetrically with respect to said first transverse heat-sealing bar.
 55. The device according to claim 45, further comprising a first longitudinal heat-sealing bar, which is arranged inside said vacuum chamber so as to correspond to said open longitudinal side of said single-folded film of the food product, a cutting blade being arranged laterally adjacent to said first longitudinal heat-sealing bar, at the outer surface of said lid there being a pair of fourth cylinders adapted to actuate a second longitudinal heat-sealing bar, which is arranged mirror-symmetrically with respect to said first longitudinal heat-sealing bar.
 56. The device according to claim 54, further comprising a plurality of holes for the return of the air into said vacuum chamber in order to return it to atmospheric pressure after the heat-sealing of a package, said plurality of holes being provided between said first transverse heat-sealing bar and the adjacent wall of said bell-shaped vacuum chamber.
 57. The device according to claim 47, wherein it is controlled by mechanical and/or electronic means for predetermining a desired position of said frame in one or more preset points, so that for each type of package it is possible to set, by means of a computer, the arrangement of said frame automatically as the package that arrives on said loading platform varies.
 58. The device according to claim 47, wherein said frame can also move transversely with respect to the direction of advancement of said single-folded film. 